Adding a tube effects loop to a Blackheart Little Giant

[StereoKills]

I've been wanting to have an effects loop on my Little Giant for a while now. From what I gather the best way to do so would be to use a tube powered loop in order to drop the voltage down to appropriate pedal levels, then boost it back up for the power amp.


I've found a few options around:

Kurt's Effects Loop for Marshal 100 & 50 watt heads
http://www.blueguitar.org/new/schem/misc_mod/fx_loop.gif

Ted Weber's Effects Loop (Got this off the net months ago, couldn't find the original posting)
http://i.imgur.com/ZM7g5.jpg

Wondering if anyone has tackled this on their own single ended amp and if someone with more tube experience could tell me which schematic would be better to follow, as they are similar.

[iccaros]

from what I know, they do not drop any voltage as high DC voltage is blocked by a coupling cap and you only get ac audio signal.
these are buffers, and do nothing for the tone of the amp. Using RGs http://www.geofex.com/Article_Folders/mosfet_folly/mosfetfolly.htm you can easily build a mosfet effects loop.

Again an effects loop is a booster setup (some times with a mixer) so tubes, transistors no difference.

Either design you posted would work

The problem with just adding a tube to the mix is that unless you know the specification for the blackhart power supply, you do not know if there is enough current left on the heater winding. Most likely, 100% sure there is, there is but I don't know.

you could go this route.. http://tknives.com/blackheart/ 

This kills me, I found it looking for the power specks for the blackheart, but it basicly replaces the blackheart with a brand new amp and calls it a upgrade kit...

[wavley]

This kills me, I found it looking for the power specks for the blackheart, but it basicly replaces the blackheart with a brand new amp and calls it a upgrade kit...

I always think this stuff is funny, I'm very guilty of sometimes throwing more work and money at something than it's worth, but if you're just gonna build a new amp it would be less work to buy a kit and build it from scratch because you don't have to disassemble it to put it together, plus the satisfaction of being able to say you built it from scratch.

[defaced]

If you do a MOSFET loop, you will need to be careful about the send and return parts. Bigger parts are better for the send, smaller parts (lower input capacitance) is better for the return. IRF820, ZVN5054(?), LND150 are all popular parts. The gross design will be easy, refining it can be challenging if you intend to remove the loop from the signal chain when its bypassed. This is what im working on with my current design.

[iccaros]

If you do a MOSFET loop, you will need to be careful about the send and return parts. Bigger parts are better for the send, smaller parts (lower input capacitance) is better for the return. IRF820, ZVN5054(?), LND150 are all popular parts. The gross design will be easy, refining it can be challenging if you intend to remove the loop from the signal chain when its bypassed. This is what im working on with my current design.

When you say "bigger" and Smaller do you mean in RDS rating?
Would not configuring the output transistor  in a cathode follower design take care of the impedance issue?

[StereoKills]

Also, what voltage/watt rating should the components be?

[Renegadrian]

http://www.webfilehost.com/?mode=viewupload&id=6201106

[StereoKills]

So that appears to just tap right into the circuit, with no buffer? I was under the impression that it was not advisable to run pedals after the signal is amplified?

[Renegadrian]

I don't know dude, I own a LG too and I guess I'll mod it with the FX loop of the pdf.

[StereoKills]

I decided to go with Kurt's design, as the second stage of the tube is actually amplifying and driving the power tube harder. Upon closer inspection of the Weber design, the second stage appears to be a buffer? (maybe someone can confirm that for me).

In the process of making a PCB in Eagle now.